This invention relates to fuel tank components and has particular reference to walls for use in self-sealing fuel tanks.
It is well-known to provide self-sealing fuel tanks for military aircraft. By virtue of their nature military aircraft are subject to penetration of projectiles such as bullets and shrapnel from exploding missiles etc. The use of a self-sealing fuel tank helps the aircraft survive in two ways. Firstly, it chokes off the escape of fuel from the fuel tank which might cause fires in the aircraft and thus destroy it. Secondly, the conventional military aricraft by virtue of the large weight of stores it has to carry has problems in providing sufficient fuel capacity. Thus, when working at long ranges the aircraft will normally only have sufficient fuel just to get back to base. If this, however, is lost as a result of enemy action the aircraft will have to be abandoned even though it is flyable. Thus, retaining the fuel in the tank by means of self-sealing tanks enables the aircraft to return to base and thus be repaired and re-used. The second feature is probably of greater importance than the first feature.
Conventional self-sealing fuel tanks have a layer of material, normally on the outside of the tank, which swells up to choke off fuel escaping from the tank. The layer may be of a type which is swellable when in contact with the fuel or may be activated by the heat of a projectile passing through it. It has been found that small diameter projectiles which leave small diameter holes can be dealt with quite adequately by swellable sealing means of this type.
However, recent advances in military technology have resulted in the use of larger diameter projectiles which can give rise to larger diameter holes. The escaping fuel through these holes has been found to pass through the hole with a sufficient velocity to wash out the expanding sealant so that the hole is never fully sealed.
In U.S. Pat. No. 4,088,240 there is described a wall for use in self-sealing tanks which is intended to help reduce problems of this type. Basically, the wall comprises a mat of thin elongate fibres arranged on the inside of the fuel tank. Once the projectile has passed through the wall the surge of escaping fuel carries with its strands of the mat adjacent the hole so as to restrict the flow of fuel through the hole.
The present invention is concerned with devices of this general type but which have improved choking characteristics compared to the prior art described in U.S. Pat. No. 4,088,240 and which may be easily and cheaply manufactured.